1. Technical Field
The present invention relates to a resonator element, a resonator, an oscillator, an electronic device, and a frequency adjustment method.
2. Related Art
In a resonator having a vibrating arm, a resonator element is known in which a vibrating arm vibrates in the thickness direction of the vibrating arm (such a mode of vibration is an out-of-plane mode) rather than vibrating in an in-plane mode. This resonator element generally has an odd number of vibrating arms. When the resonator element has three or more vibrating arms, adjacent vibrating arms perform walk-mode vibration in which they repeatedly vibrate alternately in opposing directions.
Adjustment of the frequency (resonance frequency) of a tuning-fork type resonator that vibrates in an in-plane mode is performed by providing a weight on a plane in the vibration direction of the tip end of a vibrating arm and irradiating the weight with laser light or the like to remove a part of the weight. This method performs frequency adjustment by removing a part of the weight to decrease the weight of the vibrating arm, thus sequentially increasing the frequency (see JP-A-2003-318685, for example).
In contrast, the frequency (resonance frequency) of a resonator that vibrates in an out-of-plane mode is proportional to the thickness in the vibration direction of a vibrating arm and is inversely proportional to the square of the length of the vibrating arm. Therefore, adjustment of the frequency is performed by adding a weight to the side surfaces of a vibrating arm rather than adding the weight to the surfaces defining the thickness of the vibrating arm and irradiating the weight with laser light to remove a part of the weight on the side surfaces.
When a resonator vibrating in an out-of-plane mode is miniaturized, since the length of the vibrating arm decreases, it is necessary to make the vibrating arm thin in order to obtain the same frequency.
However, it is difficult to add a weight on the side surfaces of a thin vibrating arm as in the related art. Moreover, even when the weight can be added to the side surfaces of the vibrating arm, it is very difficult to irradiate the side surfaces with laser light to remove a part of the weight. It is desirable that frequency adjustment of a resonator that vibrates in the out-of-plane mode is performed easily and with high accuracy.